{"type_number":"EF41","canonical_url":"https://tubeofile.com/tubes/EF41","manufacturer":"Philips","tube_type_key":"ss_pentode","tube_type_display_name":"Small Signal Pentode","base_name":"Rimlock","description":"Variable-mu (remote cutoff) pentode for use as R.F. and I.F. amplifier in AC receivers and car-radio sets. Gm in uncontrolled condition is 2.2 mA/V and internal resistance is 1.1 MΩ. Entire electrode system is enclosed in an internal metal shield requiring no external screening. Grid-to-anode capacitance is at most 0.002 pF.","is_directly_heated":false,"completeness":"high","notes":["Variable-mu (remote cutoff) characteristic: gm drops to 1/100th of its maximum value when Vg1 is reduced from -2.5 V to -39 V. This makes the EF41 suitable for AGC-controlled IF/RF stages.","Internal metal shield encloses the entire electrode system — no external screening is needed, but the valve must be pressed firmly into the holder and the retaining lugs on the raised metal edge of the socket must be bent slightly inward to ensure proper shield contact.","Screen grid voltage is derived via a series resistor (Rg2 = 90 kΩ) from the anode supply; screen voltage at the valve is approximately 100 V at the standard operating point (Vb = 250 V, Ig2 = 1.7 mA).","The Vs_max limit is operating-point dependent: 300 V when Ia < 3 mA (cut off by AGC), 125 V when Ia = 6 mA (normal uncontrolled condition).","Rg1_max = 3 MΩ applies when grid bias is obtained by means of a cathode (biasing) resistor. The separate Rfk_max = 20 kΩ limit applies to the external resistance between heater and cathode.","HF61 is the French Mazda designation, W150 the British Osram/GEC designation, 7F16 the French Mazda numbering, 62VP another European designation, and 6CJ5/CV3886 the JETEC/UK military designation — all electrically and pin-identical.","EF40 (Rimlock AF pentode) and EF41 share the same base but are not interchangeable: EF40 is a sharp-cutoff audio pentode while EF41 is a variable-mu RF/IF pentode. Circuit constants differ significantly."],"references":["https://tube-data.com/sheets/030/e/EF41.pdf","https://frank.pocnet.net/sheets/046/e/EF41.pdf"],"source_urls":{"r_type":"https://www.r-type.org/exhib/aad0127.htm","tdsl":"https://tdsl.duncanamps.com/show.php?des=EF41","radiomuseum":"https://www.radiomuseum.org/tubes/tube_ef41.html"},"raw_equivalents":["6CJ5","CV3886","HF61","W150","7F16","62VP"],"equivalents":[],"similar":[{"type_number":"EF40","reason":"Same Rimlock B8A base and same heater, but sharp-cutoff AF pentode vs variable-mu RF/IF pentode — different gm/ra characteristics and intended application; not a drop-in substitute without circuit redesign","has_detail_page":false},{"type_number":"EF85","reason":"Successor variable-mu RF pentode with similar characteristics but on Noval (B9A) 9-pin base — not pin-compatible with Rimlock","has_detail_page":false},{"type_number":"EF89","reason":"Successor variable-mu RF pentode with improved characteristics but on Noval (B9A) 9-pin base — not pin-compatible with Rimlock","has_detail_page":false}],"pins":[{"pin_number":"1","function":"Heater","function_code":"h","notes":null},{"pin_number":"2","function":"Anode","function_code":"a","notes":null},{"pin_number":"3","function":"Internal Connection","function_code":"ic","notes":null},{"pin_number":"4","function":"Internal Connection","function_code":"ic","notes":null},{"pin_number":"5","function":"Screen Grid","function_code":"g2","notes":null},{"pin_number":"6","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"7","function":"Cathode / Suppressor Grid (g3 internally connected to cathode)","function_code":"k","notes":null},{"pin_number":"8","function":"Heater","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"6.3","numeric_value":"6.3","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.2","numeric_value":"0.2","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Pentode","tube_type_key":"ss_pentode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"300","numeric_value":"300","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"125","numeric_value":"125","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"2","numeric_value":"2","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"0.3","numeric_value":"0.3","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"10","numeric_value":"10","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"100","numeric_value":"100","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"3","numeric_value":"3","unit":"MΩ","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"250","numeric_value":"250","unit":"V","param_group":"typical_operating"},{"key":"Vs","display_name":"Screen Voltage (typical)","value":"100","numeric_value":"100","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-2.5","numeric_value":"-2.5","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"6.0","numeric_value":"6","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"1.7","numeric_value":"1.7","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"1100000","numeric_value":"1100000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"2.2","numeric_value":"2.2","unit":"mA/V","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"<0.002","numeric_value":null,"unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"5.3","numeric_value":"5.3","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"5.9","numeric_value":"5.9","unit":"pF","param_group":"capacitances"},{"key":null,"display_name":"Rfk_max (Max resistance between heater and cathode)","value":"20000","numeric_value":"20000","unit":"Ω","param_group":null},{"key":null,"display_name":"Req (Equivalent noise resistance, uncontrolled)","value":"6500","numeric_value":"6500","unit":"Ω","param_group":null},{"key":null,"display_name":"μg2g1 (Amplification factor of screen wrt control grid)","value":"18","numeric_value":"18","unit":"—","param_group":null}]}],"synced_at":"2026-04-21T23:19:07.094Z"}